Use of non-magnetic coating for covering components in a clock movement

ABSTRACT

The present invention proposes to improve the yield of a micro-generator ( 1 ) used for operating a timepiece. This micro-generator operates on the basis of the phenomenon of electromagnetic induction; it is thus desirable to limit the presence of magnetic masses in proximity to said generator as much as possible. Research carried out has shown that the finish coating covering the movement-blank parts ( 11, 12 ) arranged in proximity to the micro-generator brakes the latter when it is made of a magnetic material, and in particular a ferromagnetic material. Thus, the exclusive selection of non-magnetic materials for manufacturing the movement-blank and its coating is proposed.

The present invention concerns a timepiece movement including inparticular an operating unit comprising magnetised masses, saidoperating unit being located at the heart of said movement and thussurrounded at least partially by non-magnetic movement-blank partscoated with a finish coating.

In particular, the present invention concerns a timepiece wherein saidoperating unit is a micro-generator.

In the following description, “non-magnetic” material means a material,which is not ferromagnetic, which is not or is only very slightlyparamagnetic, and which may have slight diamagnetism. Likewise, “inproximity to the micro-generator” means any peripheral region of themicro-generator in which the magnetic flux of the magnetised masses hasa significant value.

The operating principle of such a timepiece movement is described inparticular in Swiss Patent No. 597636 and European Patent No.851322, theteaching of which is incorporated by reference in the presentApplication. Swiss Patent No. 597636, for example, discloses a watchmovement wherein a spring drives, via a set of gears, on the one handthe hands and on the other hand, a generator generating an alternatingcurrent. The generator powers an electronic circuit comprising inparticular a stabilised quartz oscillator and enabling the working ofthe generator and thus the working of the hands, to be adjusted. Such awatch consequently combines the advantages of a mechanical watch withthe precision of a quartz watch.

However, while seeking to develop a product of this type, the Applicantobserved the existence of sources of magnetic disturbance within thewatch movement. The advantage of this type of timepiece increases whenits energy consumption decreases, i.e. when for example the generatoryield increases. With this observation as a starting point, theApplicant proved that not only ferromagnetic masses, such asmovement-blank parts or steel watch parts, but also the presence of finelayers of ferromagnetic coating on non-magnetic movement-blank parts,located in proximity to the generator, exert thereon a parasiticmagnetic force thereby reducing its yield.

The object of the present invention is thus to improve theaforementioned timepiece while avoiding the drawbacks describedhereinbefore, in particular owing to an improvement, which is simple andinexpensive to manufacture.

The invention therefore concerns a timepiece of the type indicatedhereinbefore, characterised in that said finish coating covering saidmovement-blank parts located in proximity to said operating unit hasessentially non-magnetic properties.

According to a particular embodiment of the invention, the variousmovement-blank parts are coated with a nickel-based non-magnetic alloyproviding efficient protection against the risk of oxidisation whileguaranteeing a very proper aesthetic appearance. It should be noted thatthis type of alloy has excellent adherence to the surface of themovement-blank.

In another alternative embodiment, said first nickel-based layer iscoated with a second metallic layer, in particular in order to modifythe aesthetic appearance. One may, for example, use a gold-based alloyto give the movement-blank a golden colour, which generally results in amore luxurious level of finish for the timepiece. In such case, thenickel-based first layer also has the function of a diffusion barrier,preventing the gold from diffusing into the movement-blank material.

The invention will be explained in more detail with the aid of thefollowing description of an example embodiment, made with reference tothe annexed drawings, in which:

FIG. 1 is a simplified top view of the partially mounted movement of atimepiece including a generator, and

FIG. 2 is a transverse cross-section of the movement along the lineII-II of FIG. 1.

FIG. 1 shows a view of generator 1 comprising a rotor 2 having twoflanges 3, only one of which is shown, arranged on either side of threeflat coils 4 forming the stator and offset by substantially 120 degreesin relation to each other relative to the axis of rotor 2, in a sameplane orthogonal to the latter.

Six magnets 5 are fixed radially and at regular intervals on each flange3, facing coils 4. The polarity of two consecutive magnets 5 isopposite. Moreover, the faces facing each other of the superposedmagnets 5 have opposite polarities. A printed circuit board 6 acts as asupport in particular for coils 4 and for an integrated circuit 7.

Integrated circuit 7, which is a low energy consumer, is powered byelectric micro-generator 1—formed by the assembly of shaft 8 of rotor 2,flanges 3, magnets 5 and coils 4—driven via a kinematic connection 9 bya barrel device 10. When magnets 5 pass in proximity to coils 4 thisgenerates a substantially sinusoidal induced voltage across theterminals of coils 4.

Brass movement-blank parts 11 and 12 appear in the cross-section alongline II-II of FIG. 1 shown in FIG. 2. In particular, shaft 8 of rotor 2is mounted so as to pivot in two jewels 13, 14, one of which beingdriven into a gear train-bar 11 and the other into movement plate 12.FIG. 2 clearly shows that, because of their immediate proximity tomagnets 5, said movement-blank parts 11, 12 are partially exposed to themagnetic fields of said magnets.

The Applicant has proved during his research that the fact of using aconventional magnetic material to make the finish coating for themovement-blank has a significant influence on the micro-generator yield.Astonishingly, the exclusive use of non-magnetic materials for thecoating causes a substantial decrease in magnetic disturbance, themagnetic coupling between magnetised masses 5 and coils 4 and thus theyield of micro-generator 1 being thereby increased.

The watch movement according to the invention thus includes at leastmovement-blank parts 11, 12 made of brass or any other suitable materialhaving non-magnetic properties. Moreover, in accordance with theinvention, the movement-blank is coated with a protective metal coatingagainst oxidisation. For the aforecited reasons, this metal coating isalso made of a material, which does not have magnetic properties, suchas a non-magnetic alloy of nickel with phosphorus or tin. When themovement is intended to be mounted in a timepiece of high added value, arhodium-based non-magnetic alloy can be used to make the coating of saidmovement-blank parts 11 and 12.

In an alternative embodiment, it may be desirable to make a coatingcomprising at least two layers of different materials. Indeed, if onewishes to manufacture a movement with a golden finish on themovement-blank, a first treatment should be applied to saidmovement-blank parts 11, 12 in order to coat them with a protectivesub-layer, generally made of nickel. A first protective layer againstoxidisation is thus obtained which also fulfils the function of adiffusion barrier, preventing the gold from diffusing into themovement-blank material.

Surprisingly, research has shown that even when the visible layer ismade of gold or rhodium which are non-ferromagnetic materials, thesingle magnetic nickel-based sub-layer decreases the generator yield andthus the power reserve available for the timepiece. This is why thisfine sub-layer is formed here of a non-magnetic alloy, preferablynickel-based, in accordance with the invention.

A nickel-based alloy including phosphorus may be used for this purpose,since for certain of its composition values, the alloy does not havemagnetic properties. One might use other metals to replace the nickel,such as palladium for example certain alloys of which also havenon-magnetic properties. Since the making of the finish coating itselfdoes not constitute the heart of the invention, it will not be developedin more detail in the present Application. Those skilled in the art mayrefer in particular to U.S. Pat. No. 6,099,624 disclosing examples ofalloys used in the manufacture of metallic protective coatings, alsoused for aesthetic purposes.

Multiple applications may be imagined, in the horological field, for theselection of non-magnetic materials to cover the movement-blank inaccordance with the invention. Indeed, the use of such materials wasdescribed in the case of a timepiece operating with a micro-generator,but such materials may also be used in any other type of timepiece withsensitivity to magnetic disturbance. The invention may be implemented inparticular in a timepiece wherein the operating unit is a compass, or inany other type of timepiece implementing means interacting with anexternal magnetic field, in particular for the purpose of detecting it.

1. Timepiece movement including in particular a micro-generator (1)including magnetised masses (5), said micro-generator (1) beingsurrounded at least partially by non-magnetic movement-blank parts (11,12) coated with a finish coating, characterised in that the finishcoating covering said movement-blank parts (11,12) located in proximityto said micro-generator (1) has essentially non-magnetic properties. 2.Timepiece movement according to claim 1, characterised in that saidcoating includes at least two metallic layers of which at least thelayer which is directly in contact with said movement-blank parts (11,12) contains nickel as a non-magnetic alloy constituent.
 3. Timepiecemovement according to claim 1, characterised in that saidmicro-generator (1) includes a rotor (2) including two flanges (3) eachsubstantially disc-shaped and each carrying, on its face opposite theother flange, an even number of magnetised masses (5), saidmicro-generator further including an electronic module (6) including atleast a stator coil (4) partially inserted between the two flanges (3)and in that said micro-generator is at least partially located in avolume delimited by the orthogonal projections of said non-magneticmovement-blank parts (11, 12).
 4. Timepiece movement including inparticular an operating unit (1) including magnetised masses (5) andallowing the presence of an external magnetic field to be detected, saidoperating unit (1) being surrounded at least partially by non-magneticmovement-blank parts (11, 12) coated with a finish coating,characterised in that the finish coating covering said movement-blankparts (11, 12) located in proximity to said operating unit (1) hasessentially non-magnetic properties.
 5. Timepiece movement according toclaim 4, characterised in that said operating unit has the function of acompass.